Fix outstanding UX issues with replies/mentions/keyword notifs (#28270)

* Fix outstanding UX issues with replies/mentions/keyword notifs

* Use createRoot instead of deprecated ReactDOM.render

I foresee this change being made across the codebase shortly
and want to proactively prevent my PR from falling behind

* Clean up react root on unmount

* Remove addition of left-edge highlight on message mentions

It is clear that it would be best for me to address
this piece in a separate PR.

* Update call to ReactRootManager.render

---------

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

test/unit-tests/components/views/messages/TextualBody-test.tsx

@@ -7,7 +7,7 @@ Please see LICENSE files in the repository root for full details.
 */
 
 import React from "react";
-import { MatrixClient, MatrixEvent } from "matrix-js-sdk/src/matrix";
+import { MatrixClient, MatrixEvent, PushRuleKind } from "matrix-js-sdk/src/matrix";
 import { mocked, MockedObject } from "jest-mock";
 import { render, waitFor } from "jest-matrix-react";
 
@@ -228,6 +228,23 @@ describe("<TextualBody />", () => {
             const content = container.querySelector(".mx_EventTile_body");
             expect(content.innerHTML.replace(defaultEvent.getId(), "%event_id%")).toMatchSnapshot();
         });
+
+        it("should pillify a keyword responsible for triggering a notification", () => {
+            const ev = mkRoomTextMessage("foo bar baz");
+            ev.setPushDetails(undefined, {
+                actions: [],
+                pattern: "bar",
+                rule_id: "bar",
+                default: false,
+                enabled: true,
+                kind: PushRuleKind.ContentSpecific,
+            });
+            const { container } = getComponent({ mxEvent: ev });
+            const content = container.querySelector(".mx_EventTile_body");
+            expect(content.innerHTML).toMatchInlineSnapshot(
+                `"<span>foo <bdi><span tabindex="0"><span class="mx_Pill mx_KeywordPill"><span class="mx_Pill_text">bar</span></span></span></bdi> baz</span>"`,
+            );
+        });
     });
 
     describe("renders formatted m.text correctly", () => {